1. Field of the Invention
This invention relates to optical fibers and more particularly to optical fibers comprising a fluorine-containing core.
2. Description of the Related Art
Optical fibers have received widespread interest for information and data transfer. Fiber-guided modulated light beams are useful in many applications, for example, telecommunications, computer link-ups, and automotive controls. Advantageously, fiber optic linkages have a greater information carrying capacity as compared to metal wires carrying electrical signals. Furthermore, fiber optics are less likely to suffer from external interference, such as electromagnetic radiation.
Typically, optical fibers comprise a light carrying core, for example an inorganic glass such as fused silica or a polymer such as polymethyl methacrylate, and a cladding material having a lower refractive index than the core. The cladding material serves to confine the light energy within the core and thereby allows propagation of light by a phenomenon generally known as "total internal reflection."
Characteristically, glass optical fiber cores have very low optical loss and are generally preferred for long distance applications. On the other hand, the cost of connecting glass optical fiber cores tend to be cost prohibitive for short distance, connector intensive applications. Polymer fibers overcome the cost limitation for short distances. Furthermore, they are lighter weight, more flexible, and have a larger diameter than glass fibers. Although polymer fibers exhibit a greater optical loss than glass core fibers, they are preferred in shorter length applications. The most common commercial polymer optical fiber core material is polymethyl methacrylate (PMMA).
EPO 250,996 describes .alpha.- and .beta.-fluorinated acrylates and methacrylates as cladding materials for glass core optical fibers.
EPO 256,765 describes .alpha.- and .beta.-fluorinated acrylates and methacrylates as cladding for polymer core optical fibers.
T. Kaino, "Recent Development in Plastic Optical Fibers", in Frontiers of Macromolecular Science, edited by Saegusa et al, page 475, describes deuterated polymer optical fibers and deuterated-fluorinated polymer optical fibers. Deuteration, or deuterium substitution for some of the hydrogen atoms, is not cost effective, and the deuterated polymer is still subject to optical degradation as a function of increasing environmental humidity.
Makromol. Chem., 189, p2861, 1988, W. Groh, "Overtone Absorption in Macromolecules for Polymer Optical Fibers", a paper describing molecular bond absorption, concludes that perfluorinated polymers should show low optical loss.
Kokai No. JP60-258281 (English translation) describes optical lenses consisting of copolymers of at least one polymerizable compound containing polyfluoroalkyl methacrylates and non-fluorinated methacrylates.
Kokai No. JP57-190902 (English translation) describes optical fibers constructed of a core material of fluoroalkyl methacrylates, or copolymers of both fluorinated and non-fluorinated acrylates and methacrylates. The largest fluoroalkyl moiety disclosed was pentyl.
Japanese Patent No. 62-208005 (English translation) describes optical fibers formed from polymers expressed by the general formula ##STR1## wherein R.sup.1 is a hydrogen atom, or C.sub.1-3 alkyl groups, X is a halogen atom and m is an integer of 1-5.
U.S. Pat. No. 4,500,694 describes optical fibers produced from fluoroalkyl acrylates and methacrylates with a fluorinated alkyl moiety of up to 3 carbon atoms, and copolymers of these fluoroalkyl groups with both fluorinated and non-fluorinated acrylates and methacrylates.